DE102022108474B4 - Method and measuring camera for measuring a surface profile of an object - Google Patents

Abstract

Method for measuring a surface profile of an object (26, 26'), the method comprising the following steps: a) providing a measuring camera (24) which has an image sensor (36) and a lens (38) which is telecentric at least on the object side, wherein the Lens (38) an object plane (O), a first optical subsystem (L1), a second optical subsystem (L2; L21, L22), one between the first optical subsystem (L1) and the second optical subsystem (L2; L21, L22 ) arranged pupil plane (42) and an image plane (B) in which the image sensor (36) is arranged; b) recording a first image of the object (26, 26 '), with only light contributing to the first image illuminating a first area (A1) of the pupil plane (42);c) recording a second image of the object (26, 26') with the same relative arrangement between the object (26, 26') and the measuring camera (24), whereby only Light contributes to the second image, illuminating a second area (A2) of the pupil plane (42), which differs from the first area (A1), and wherein at least one of the two areas (A1, A2) is not point-symmetrical with respect to an optical axis (52) of the objective (38);d) calculating the surface profile of the object (26, 26') with respect to the optical axis (52) of the objective (38) from a lateral offset between structures (S1, S2, S3) on the first image and corresponding structures (S1, S2, S3) on the second image, characterized in that the second optical subsystem has two optical elements (L21, L22) which are in a direction perpendicular to the optical axis (52) of the objective (38 ) are arranged next to each other and divide the beam path into two separate partial beam paths, and that steps b) and c) are carried out simultaneously.

Description

BACKGROUND OF THE INVENTION

1. Field of the invention

The invention relates to a method and a measuring camera for measuring a surface profile of a workpiece or another object according to the preamble of claim 1 or claim 6. Such a method and such a measuring camera are from DE 10 2017 115 021 A1 known. A surface profile is understood to be the set of all z coordinates of selected points with coordinates (x, y) on a surface of the object facing the measuring camera, with the z direction running parallel to the optical axis of the measuring camera.

2. Description of the prior art

In the prior art, coordinate measuring machines are used to measure the geometry of workpieces. Such measurements take place, for example, as part of quality assurance or so-called “reverse engineering”. The sometimes complex measurement tasks are usually reduced to measuring the spatial coordinates of a number of individual points.

The coordinate measuring machines contain a sensor whose position can be changed relative to the workpiece to be measured using drives. Especially with smaller coordinate measuring machines, the workpiece is located on a cross table that can be moved along two horizontal coordinate axes x, y with high accuracy. The sensor is usually attached to a quill, which can be moved vertically (i.e. in the z direction) with a similarly high level of accuracy. If particularly large or heavy workpieces are to be measured, portal-type coordinate measuring machines are used, in which the workpiece is stationary and only the sensor is moved.

When it comes to sensors for coordinate measuring machines, a distinction is made between optical and tactile sensors. While with tactile sensors the information about the position of a measuring point is generated by touching the measuring point with a probing element, with optical sensors the information about the position of the measuring point is transmitted by light.

In one type of optical sensor, the z coordinates of the workpiece surface are determined using the autofocus method. For this purpose, the sensor has a measuring camera with a lens and an image sensor. If the quill with the sensor attached to it is moved vertically along the optical axis of the lens, a sharp image of those areas of the surface of the workpiece that are at the same height is only generated in a z position of the measuring camera. Outside this position, the image sensor is defocused, so that these surface areas appear blurry in the captured images.

In optical coordinate measuring technology, contrast is used as a parameter for the sharpness of the images created on the image sensor. The contrast for a specific point on the surface of the workpiece is maximum when the point is located exactly in the object plane of the measuring camera lens. Since the position of the object plane in a reference system of the coordinate measuring machine is known with high precision, the distance to this point and thus its z coordinate can be measured very precisely in this way. The faster the contrast drops when the point moves out of the object plane, the higher the accuracy of this measurement.

In order to carry out a 3D coordinate measurement for a specific workpiece using the autofocus method, a relative movement must be generated between the workpiece and the object plane along the optical axis of the lens. For this purpose, either the workpiece, the measuring camera or both can be moved in the z direction. Alternatively or additionally, the position of the object plane can be changed by moving individual lenses of the objective or with the help of an optical element with variable refractive power (e.g. a liquid lens). The images of the workpiece surface taken at different times during the relative movement are saved in order to then calculate the 3D coordinates of the workpiece surface using the contrast determination. From the images in which certain areas of the workpiece surface are sharply reproduced, edges and other contours can also be determined using image processing algorithms and correlated with the measured z coordinates.

Coordinate measuring machines that calculate the z coordinates according to the principle of the autofocus method explained above are sold by the applicant under the trademark ZEISS O-INSPECT and are available, for example, in DE 10 2016 202 928 A1 described.

Measuring cameras in such optical sensors are usually telecentric at least on the object side. Bundles of rays that emanate from points in the object plane and from the aperture of the The measuring camera recorded runs parallel to the optical axis. Telecentric lenses on the object side in measurement cameras are particularly advantageous because the magnification scale does not depend on the distance of the object. An object that is outside the object plane will be blurred onto the image plane, but the resulting blurred image will still be the same size as the sharp image obtained if the object is in the object plane.

Since the distance between the image sensor and the optics of the measuring camera is fixed, telecentricity on the image side could basically be dispensed with. Nevertheless, measurement cameras are usually telecentric on both sides to ensure that drift movements of the image sensor as a result of temperature fluctuations or aging do not lead to measurement errors.

From an essay KIM, Jun-Sik ; KANADE, Takeo: Multiaperture telecentric lens for 3D reconstruction. In: Optics Letters, Vol. 36, 2011, No. 7, pp. 1050-1052. - ISSN 0146-9592 (P); 1539-4794 (E). DOI: 10.1364/OL.36.001050. Double-sided telecentric lenses for measuring cameras are known, in which a second off-axis aperture opening is provided in the pupil plane, which is often also referred to as the aperture or aperture plane, in addition to a first aperture opening on the optical axis. In this way, distance information between the measuring camera and the object can be determined.

The possibility of arranging different apertures in the pupil plane and thus achieving variable pupil filtering is also occasionally used in other measurement cameras. The different aperture elements are usually accommodated in an automatic exchange unit, which can be designed, for example, as a turret holder. However, the replacement units are mechanically complex, require a lot of installation space and do not enable a quick change in the light distribution in the pupil plane.

From the US 2008/0239316 A1 A measuring camera is known which uses an LCD panel arranged in the pupil plane for the purpose of pupil filtering. Such panels require very little installation space and have a switching speed that is usually less than 5 µs. However, LCD panels polarize the incident light. This is disadvantageous for certain applications and is also accompanied by intensity losses, which can lead to a lower signal-to-noise ratio on the image sensor and thus to less accurate measurement results.

From an article SHEPARD, R. Hamilton [et al.]: Optical design and characterization of an advanced computational imaging system. In: Optics and Photonics for Information Processing VIII: 18-20 August 2014, San Diego, California, United States. Bellingham, Wash. : SPIE, 2014 (Proceedings of SPIE ; 9216). Item number: 92160A (p.1-15). - ISBN 978-1-62841-243-7. DOI: 10.1117/12.2060725. a test stand with a simultaneously pupil- and time-coded imager is known, which uses a DMD (Digital Mirror Device) for the purpose of pupil apodization or a deformable mirror for wavefront coding experiments.

The printed matter US 2012/0154571 A1 , DE 10 2021 118 327 A1 (post-published) and DE 10 2021 118 429 A1 (also subsequently published) disclose optical systems that have a switchable filter element in the pupil plane.

From the JP S58-194007 A and the US 2002/0060793 A1 Devices for determining distances are known in which adjustable devices in the pupil plane are used.

SUMMARY OF THE INVENTION

The object of the invention is to provide a method and a measuring camera with which a surface profile of an object can be optically measured very quickly.

With regard to the method, this task is solved by a method according to claim 1.

The idea behind this procedure is that a non-point-symmetrical trimming of the beam path in the pupil plane leads to the image of a defocused object moving in the image plane of the measuring camera. So if you take two images, with at least one of the two (not necessarily contiguous) illuminated areas in the pupil plane not being illuminated point-symmetrically with respect to the optical axis of the lens, the defocusing and thus the defocusing can be determined from the lateral offset of the two images Close z position of the relevant points on the surface of the object. Since the lateral coordinates of the edges can also be calculated, the entire surface profile of the object can be derived from just two images.

When taking the two images, the relative arrangement between the object and the measuring camera remains the same, and the position of the object plane is not changed by movements within the measuring camera. This allows the Ober According to the invention, surface profile can be measured particularly quickly.

The method according to the invention has similarities with the phase comparison method that is used in high-quality photo cameras for autofocusing (AF). There, images of the object are recorded by AF sensors arranged in pairs and diametrically opposed to each other and the defocusing is calculated from a lateral offset of the images. However, the AF sensors only capture very small sections of the images that are then captured by the main image sensor. It is therefore not possible to measure a surface profile with such photo cameras.

With the method according to the invention, however, it is possible to measure the surface profile even for large surfaces. The fact that this is possible is due to the fact that in the measuring camera according to the invention the pupil plane is arranged between the two optical subsystems and is therefore easily accessible. This allows the light path to be divided directly in or near the pupil plane without having to compromise on the size of the two captured images. In photo cameras, on the other hand, the pupil plane offers little space and is not easily accessible. In addition, the aperture cannot be adjusted so that at least one of the two areas in the pupil plane is not point-symmetrical with respect to the optical axis of the lens. A comparable effect can only be achieved with photo cameras by making the image section captured by the AF sensors appropriately small.

1. e) Bestimmen eines Steuersignals für einen Verstellvorgang auf der Grundlage des in Schritt d) berechneten Oberflächenprofils, wobei durch den Verstellvorgang der Abstand zwischen dem Objekt und der Objektebene so verändert wird, dass sich eine ausgewählte Ebene des Objekts in der Objektebene befindet;
2. f) Aufnehmen eines Messbildes mit Hilfe des Bildsensors, wobei zur Entstehung des Messbildes Licht beiträgt, das einen Bereich der Pupillenebene ausleuchtet, der größer ist als der erste Bereich und der zweite Bereich.

If necessary, knowing the defocusing by changing the lens and/or the distance between the measuring camera and the object, the object can be moved into the object plane of the object in order to then obtain a sharp image, on the basis of which the x and y coordinates can be determined. The procedure can include the following additional steps:

1. e) determining a control signal for an adjustment process based on the surface profile calculated in step d), the adjustment process changing the distance between the object and the object plane so that a selected plane of the object is in the object plane;
2. f) Recording a measurement image with the aid of the image sensor, with light contributing to the creation of the measurement image, which illuminates an area of the pupil plane that is larger than the first area and the second area.

In the parts of the measurement image recorded in this way that are imaged in focus, the lateral dimensions can be recognized particularly precisely by image processing algorithms. The large aperture with which the measurement image was recorded contributes to the increased resolution.

For the measurement of the z coordinates, it would be sufficient if the pupil plane was illuminated point-symmetrically (in particular, rotationally symmetrically in a special case) when taking an image and if a non-point-symmetrical area was illuminated only when taking the other image. The recording with the point-symmetrical illumination would then provide the required reference point for the offset measurement.

However, a higher measurement accuracy can be achieved if neither of the two illuminated areas is point-symmetrical with respect to the optical axis, but one of the two areas is point-symmetrical to the other of the two areas with respect to the optical axis. This way the images are offset by the same amount in opposite directions. This means that two identical but opposite offset distances add up, resulting in a gear ratio between lateral offset and focus offset that is twice as large.

According to the invention, the second optical subsystem has two optical elements which are arranged next to one another in a direction perpendicular to the optical axis of the objective and divide the beam path into two separate beam paths. Steps b) and c) can then be carried out simultaneously.

The two optical elements, which preferably have a collecting effect and can be designed, for example, as simple lenses, separate the beam path so that the two images are created on the image sensor simultaneously and next to each other. This further shortens the measurement time because both images can be taken at the same time. Although the images have the same large image section, they are smaller compared to a variant with a variable pupil filter, which leads to a certain loss in image quality and thus also in measurement accuracy.

Especially with regard to the independence of direction, it can be advantageous if the first optical subsystem has not just two, but three or in particular four optical elements, which are arranged, for example, at the corners of a regular triangle or a square.

In a further development, the measuring camera has an additional image sensor and a beam splitter, which is arranged between the first optical subsystem and the second optical subsystem. The beam splitter divides the beam path into a first beam path leading to the image sensor and a second beam path leading to the further image sensor. With the help of the additional image sensor, an additional large measurement image can be recorded at the same time, which can be used, for example, to determine the lateral dimensions of the structures visible in the images more precisely.

With regard to the device, the task posed at the beginning is solved by a measuring camera according to claim 6.

It is preferred if the lens is also telecentric on the image side. A lens that is telecentric on both sides theoretically has no distortion or other geometric aberrations.

With regard to the advantageous configurations, reference is also made to the comments on the method.

BRIEF DESCRIPTION OF THE DRAWINGS

• 1: eine perspektivische Darstellung eines Koordinatenmessgeräts mit einer erfindungsgemäßen Messkamera;
• 2: einen meridionalen Schnitt durch die in der 1 gezeigte Messkamera gemäß einer nicht erfindungsgemäßen Variante, bei der in einer Pupillenebene ein LCD-Panel als variabel einstellbares Pupillenfilter angeordnet ist;
• 3a und 3b: einen Strahlengang in der Messkamera für zwei unterschiedliche Objektweiten;
• 4a und 4b: den 3a und 3b entsprechende Darstellungen für den Strahlengang bei zwei hintereinander mit der Messkamera aufgenommenen Bildern;
• 5a bis 5c: Blendenöffnungen bei den mit der Messkamera aufgenommenen Bildern;
• 6a und 6b: ein beispielhaftes Objekt in einer Draufsicht bzw. einer Seitenansicht;
• 7a und 7b: zwei von der Messkamera mit unterschiedlichen Blendeneinstellungen aufgenommene Bilder;
• 8a und 8b: den 4a und 4b entsprechende Darstellungen, bei denen anderen Blendeneinstellungen vorgenommen wurden;
• 9a bis 9c: Blendenöffnungen für mit der Messkamera aufgenommene Bildern gemäß den in den 8a und 8b gezeigten Blendeneinstellungen;
• 10: einen der 2 entsprechenden meridionalen Schnitt durch eine nicht erfidungsgemäße Messkamera gemäß einer zweiten Variante, bei der das variable Pupillenfilter als digitales Mikrospiegelarray ausgebildet ist;
• 11: einen den 3a und 3b entsprechenden meridionalen Schnitt durch eine erfindungsgemäße Messkamera;
• 12: die Blendenausleuchtung bei der in der 11 gezeigten Messkamera;
• 13: eine Variante der in der 11 gezeigten Messkamera mit einem Strahlteiler und einem zusätzlichen Bildsensor zur gleichzeitigen Aufnahme eines Messbildes.

Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. Show in these:

• 1 : a perspective view of a coordinate measuring machine with a measuring camera according to the invention;
• 2 : a meridional section through the in the 1 measuring camera shown according to a variant not according to the invention, in which an LCD panel is arranged as a variably adjustable pupil filter in a pupil plane;
• 3a and 3b : a beam path in the measuring camera for two different object widths;
• 4a and 4b : the 3a and 3b Corresponding representations of the beam path for two images taken one after the other with the measuring camera;
• 5a to 5c : Aperture openings in the images taken with the measuring camera;
• 6a and 6b : an exemplary object in a top view or a side view;
• 7a and 7b : two images captured by the measurement camera with different aperture settings;
• 8a and 8b : the 4a and 4b corresponding representations in which different aperture settings were made;
• 9a to 9c : Aperture openings for images taken with the metering camera according to the values specified in the 8a and 8b aperture settings shown;
• 10 : one of the 2 corresponding meridional section through a measuring camera not according to the invention according to a second variant, in which the variable pupil filter is designed as a digital micromirror array;
• 11 : one the 3a and 3b corresponding meridional section through a measuring camera according to the invention;
• 12 : the aperture illumination at the in the 11 measuring camera shown;
• 13 : a variant of the one in the 11 Measuring camera shown with a beam splitter and an additional image sensor for simultaneously recording a measurement image.

DESCRIPTION OF PREFERRED EMBODIMENTS

1. Construction of a coordinate measuring machine

The 1 shows a perspective view of a coordinate measuring machine designated 10. The coordinate measuring machine 10 includes a base 12 which carries a table 14 to which a control panel 16 is attached. Starting from the table 14, a stand 18, which carries a quill 20, extends upwards. As indicated by a double arrow 22, the quill 20 can be moved precisely in the vertical direction (z direction) with the aid of a drive, not shown.

A measuring camera 24 is attached to the underside of the quill 20, with which an image of a workpiece 26 can be recorded. The workpiece 26 is mounted on a cross table 28, with which the workpiece 26 can be moved precisely in the horizontal plane (x-direction and y-direction), as in the 1 is indicated by arrows 30 and 32, respectively. In this way, it is possible to successively measure even larger workpieces 26 using the measuring camera 24 by gradually introducing the workpiece 26 into the measuring field of the measuring camera 24 using the cross table 28.

If even larger or particularly heavy workpieces 26 are to be measured, the coordinate measuring machine 10 can also have a different mechanical structure and, for example, instead of the cross table 28, have a movable portal to which the quill 20 is attached. In this way, the quill 20 can be moved precisely not only along the z-direction, but also along the x-direction and y-direction, as is the case in State of the art is known. The workpiece 26 then does not have to be moved during the measurement.

2. Structure of the measuring camera

The 2 shows a simplified meridional section of the structure of the measuring camera 24 according to a first exemplary embodiment. The measuring camera 24 has a two-dimensional image sensor 36 arranged in an image plane B, which can be a conventional CCD sensor or CMOS sensor. The measuring camera 24 also includes a lens 38, which has a first optical subsystem L1 and a second optical subsystem L2. The two optical subsystems are in the 2 indicated as individual lenses, but can also include several lenses or other optical elements.

The lens 38 is telecentric on both sides, so that the main rays H run parallel to the optical axis 52 of the lens 38 both in the object space and in the image space. In the exemplary embodiment, this is caused by the rear focal plane of the first optical subsystem L1 coinciding with the front focal plane of the second optical subsystem L2. In the 2 the focal lengths of the two optical subsystems L1 and L2 are denoted by f ₁ and f ₂ , respectively. If the focal lengths f ₁ and f ₂ are identical, the lens 38 has a 4f construction and a magnification ratio of 1:1. As a result of the bilateral telecentricity, the image that is created by an object 26 on the image sensor 36 in the image plane B is distortion-free. Structures outside the object plane O are imaged less sharply, but with the same magnification.

The pupil plane 42 of the lens 38 is located in the rear focal plane of the first optical subsystem L1, which, as already mentioned, coincides with the front focal plane of the second optical subsystem L2. A variably adjustable pupil filter in the form of an LCD panel 44 is arranged in the pupil plane 42. For this purpose, the LCD panel 44 comprises a large number of liquid crystal cells 46 arranged in a matrix, the transmittance of which can be changed individually between a minimum value near 0% and a maximum value near 100%. Im in the 2 In the mode shown, all liquid crystal cells 46 are maximally translucent, so that the numerical aperture is only limited by the edge 47 of the LCD panel.

A lighting device 50 is integrated into a housing 48 of the measuring camera 24, which in the exemplary embodiment shown comprises several LEDs which are arranged in a ring around the optical axis 52 of the lens 38. The lighting device 50 can, for example, be designed so that it can direct light with different colors and/or from adjustable directions onto the surface 40 of the workpiece 26. An example of a suitable lighting device 50 is in the WO 2013/167168 A1 described by the applicant. In addition to the illumination in reflected light, a further illumination device can be provided with which measuring light is coupled into the beam path of the lens 38 via a coupling mirror in order to be able to illuminate the measuring field directly from above and approximately parallel to the axis. In certain versions, illumination in transmitted light is also possible.

At 53 is in the 2 a drive is indicated, with which the quill 20 with the measuring camera 24 attached to it can be moved vertically along the z-direction, as indicated by the double arrow 22. Since the quill 20 in the 2 is not shown, the drive 53 is shown as if it were acting directly on the measuring camera 24. In reality, however, the drive 53 acts on the quill 20.

The image sensor 36, the LCD panel 44, the lighting device 50, the drive 53 and the cross table 28 are connected to a computing unit 54, which contains a memory 55, controls the measurement process in a manner to be explained in more detail and the images recorded by the image sensor 36 processed.

3. Function

To explain the function of the measuring camera 24, first refer to the 3a and 3b Referenced. These figures show the essential optical elements of the measuring camera 24 in the event that only one off-axis liquid crystal cell of the LCD panel 44 is translucent and all other liquid crystal cells 46 have a transmittance of almost 0%. This transparent liquid crystal cell defines an area A1 through which measuring light can pass and which therefore represents an aperture.

If the surface of the object 26 indicated by solid lines is in the object plane O, the image of the surface created on the image sensor 36 is centered with respect to the optical axis 52, as shown in FIG 3a is indicated with solid lines. In the case of an object 26' arranged outside the object plane O, the light rays do not pass through the area A1 parallel to the optical axis 52, but rather inclined to it. This results in a lateral offset of the image by the distance d ₁ , as shown in the 3a is indicated by the beam path indicated by dashed lines. A comparison of the 3a and 3b further shows that the further away the object 26' is from the object plane O (Δz ₂ > Δz ₁ ), the larger the lateral offset becomes (ie d ₂ > d ₁ ).

With the one in the 3a and 3b In the case shown, the object distance of the object 26' is greater than the focal length f ₁ of the first optical subsystem L1, in which the object plane O is located. However, if the object distance is smaller than the focal length f ₁ , the image is created with a lateral offset in the opposite direction. The direction in which the offset takes place is also determined by the location of the transparent area A1 (aperture), which in the illustrated embodiment is determined by the LCD panel 44. The direction of the lateral offset d of the images on the image sensor 36 lies in a plane that is spanned by the area A1 (aperture) and the optical axis 52.

It can be shown that for small numerical apertures NA of the objective 38 there is a linear relationship between the lateral offset d on the one hand and the axial distance between the object 26 and the object plane O on the other hand, which is referred to below as defocusing Δz. This relationship is used to measure the axial distance of structures on the object 26 to the known position of the object plane O.

The 4a and 4b illustrate an exemplary embodiment of a measuring process in the 3a and 3b related representations.

In a first step, a first image of the object 26 is recorded, with only light contributing to the first image, illuminating a first off-axis region A1 of the pupil plane 42. For this purpose, the computing unit 54 controls the LCD panel 44 in such a way that only a small strip-shaped off-axis area A1 can be penetrated by the measuring light. The area A1 is in the 5a shown, which shows a top view of the LCD panel 44. All structures on the object 26 with the same defocus Δz are laterally offset by the amount d in the recorded image. Structures with a different defocus are laterally offset by a correspondingly different amount.

In a second step, a second image of the object 26 is recorded with the same relative arrangement between the object 26 and the measuring camera 24. Only measuring light that illuminates a second area A2 in the pupil plane 42, which differs from the first area A1, contributes to the second image. In the exemplary embodiment shown, the second area A2 is arranged point-symmetrically with respect to the optical axis to the first area A1, as is the case in a comparison 5a and 5b shows.

All structures on the object 26 with the same defocus Δz are laterally offset by the amount d in the second image, but now in the opposite direction, cf. 4b . A comparison of the two images thus leads to a lateral distance of the structures visible in the images with the same defocusing by the amount 2d, from which the value for the defocusing Δz results.

The 6a , 6b and 7a, 7b illustrate this connection using a simple example. The 6a and 6b show a simply constructed object 26 in a top view or in a side view. The object 26 is composed of three cuboid bars R1, R2 and R3, the differently designed surfaces S1, S2 and S3 (cf. 6a) and have different dimensions in the z and x directions.

It is now assumed that the object 26 is delivered to the measuring camera 24 in such a way that the surface S3 of the bar R3 is located exactly in the object plane O of the measuring camera 24, as in the 6b is indicated. The surface S1 of the bar R1 is then arranged closer to the measuring camera 24 and the surface S2 of the bar R2 further away from the measuring camera 24.

The 7a and 7b show the two images of the object 26 as they are recorded with the measuring camera 24 in the manner described above. Since the surface S3 is located in the object plane O, it appears in the two images without any lateral offset.

The surface S1 is located closer to the measuring camera 24 and is therefore shown offset to the left in one image and to the right in the other image, as shown 7a and 7b illustrate. In the case of the surface S2 of the bar R2, which is arranged further away from the measuring camera 24, the images of the surface S2 are offset in opposite directions and also by a smaller amount, since the distance between the surface S2 and the object plane O is smaller in magnitude than in the case of the surface S2 Surface S1.

The computing unit 54 can use the images according to 7a and 7b completely reconstruct the object 26 and in particular derive the z coordinates of the surfaces S1, S2 and S3 from the respective offset with which the surfaces S1, S2 and S3 appear on the two images.

This example also makes it clear that for the image processing algorithms the upper Areas S1, S2 and S3 must generally be identifiable. In particular, structures on the surfaces S1, S2, S3 should run at an angle to the offset direction, since otherwise it may be difficult or impossible to detect the offset of the images of the structures in the two recorded images.

The requirement of recognizability may make it necessary to adapt the position of the transparent areas A1, A2 in the pupil plane 42 to the orientation of the structures on the surface of the object 26.

In many cases, individual adjustment can be avoided if not two, but four images of the object 26 are recorded. In the two additional images, the apertures A1 and A2 are arranged in a manner as can be seen by rotating the in the 5a and 5b shown arrangement can be obtained by 90 °. The images of the surfaces S1, S2, S3 in the 6a and 6b Object 26 shown would then not be the same as in these two additional images 7a and 7b shown along the x direction, but offset along the y direction.

4. Variants and further exemplary embodiments

The 8a and 8b show in to the 4a and 4b Figures based on a variant in which the aperture openings A1 and A2, which are selected for the first and second images, are not point-symmetrical to one another with respect to the optical axis 52. Instead, a rotationally symmetrical aperture A1 is used in an image, as shown in the 9a is illustrated. The structures on the object 26 are therefore without lateral offset, i.e. centered on the optical axis 52, shown.

The other image is recorded with an aperture A2, which is not arranged point-symmetrically to the aperture A1 with respect to the optical axis 52, as is the case 9b illustrated. In this variant, however, the offset of structures with the same defocusing on the two images is only d and not 2d, which has a disadvantageous effect on the measurement accuracy.

The measurement camera 24 makes it possible to record an additional measurement image, which is recorded with a larger or maximum large transparent area A3 (aperture) and a correspondingly shallow depth of field, as is the case 5c and 9c illustrate. Due to the large aperture opening, such an additional measurement image has a higher resolution than the images taken with the ones in the 5a , 5b and the aperture openings shown in FIGS. 9a and 9b were recorded. The lateral dimensions of the structures on the object 26' can be recorded even more precisely on such an additional measurement image. To generate the additional measurement image, only the LCD panel 44 needs to be controlled accordingly by the computing unit 54. The order in which the images are taken does not matter.

Due to the smaller depth of field, only those structures that are located in the object plane O are shown sharply on the measurement image. However, based on the measured surface profile, it is possible to calculate control signals for an adjustment process with which the distance between the object 26 and the object plane O is changed so that any selected plane of the object 26 is in the object plane O. In the exemplary embodiments described so far, the adjustment process is carried out by the drive 53 acting on the quill 20. This autofocusing allows those structures that are in the object plane O after the adjustment process to be sharply imaged and measured using image processing algorithms. In particular, it is possible to record several measurement images one after the other at different object distances.

The 10 shows an exemplary embodiment in which the measuring camera 24 contains a micromirror array 44 'instead of an LCD panel 44, which is also arranged in the pupil plane 42. For this purpose, the measuring camera 24 has an additional deflecting mirror 63, so that the beam path is deflected twice by 90 ° by reflection on the deflecting mirror 63 and the micromirror array 44 '.

The micromirror array 44' has a plurality of micromirrors 64, each micromirror 64 having an active position in which incident light is deflected by 90° and thereby directed in the direction of the image sensor 36. In an inactive position, incident light is deflected by such a large angle that it does not fall on the image sensor 36 but on a light absorber 65. By specifically adjusting the micromirrors 64, similar to the LCD panel 44, the aperture openings (areas A1, A2 and A3) can be set arbitrarily within wide limits and changed within a few microseconds.

The 11 shows a further exemplary embodiment in which the aperture openings cannot be changed variably. In this exemplary embodiment, the second optical subsystem L2 is replaced by two subsystems, which are indicated by smaller individual lenses L21, L22 with the same refractive power. The two sub-systems L21, L22 are in a direction perpendicular to the optical axis 52 arranged next to each other and divide the beam path into two separate partial beam paths. Like in the 12 is indicated by dashed lines, the light of each partial beam path only passes through an off-axis region A1 or A2 in the pupil plane 42, the regions A1 and A2 being arranged point-symmetrically with respect to the optical axis 52. This creates a similar effect to that in the 4a and 4b shown embodiment. Two images are thus created on the image sensor 36, which are offset in opposite directions by the amount d with respect to the respective optical axis of the sub-system L21, L22. Defocusing Δz can be calculated from the offset d.

The advantage of this exemplary embodiment is that the two images are created simultaneously on the image sensor 36, which leads to a further reduction in the measurement time. In this exemplary embodiment, the aperture openings cannot be set variably and in particular cannot be adapted to the orientation of structures on the object 26, as is the case with the previously described embodiments.

In order to achieve the greatest possible independence from the structural directions on the object, instead of two lenses L21, L22, four or more lenses can also be arranged next to one another in a direction perpendicular to the optical axis 52. For example, four lenses can be arranged so that the lens centers rest on the corners of an imaginary square.

It goes without saying that instead of individual lenses L21, L22, more complex optical subsystems, each with several optical elements, can also be used.

An additional measurement image with a wide or maximum aperture can be created using the one in the 11 However, the measuring camera 24 shown does not generate it.

The 13 shows a variant of the one in the 11 shown structure, in which a beam splitter 70 is arranged near the pupil plane 42 - and thus between the first optical subsystem L1 and the two lenses L21, L22 of the second optical subsystem. The beam splitter 70 divides the beam path into a first beam path leading to the image sensor 36 and a second beam path leading to a further image sensor 36 '. The second image sensor 36 'is intended to record a measurement image with a larger numerical aperture at the same time as the offset images recorded by the image sensor 36.

Claims (7)

Method for measuring a surface profile of an object (26, 26'), the method comprising the following steps: a) providing a measuring camera (24) which has an image sensor (36) and a lens (38) which is telecentric at least on the object side, wherein the Lens (38) an object plane (O), a first optical subsystem (L1), a second optical subsystem (L2; L21, L22), one between the first optical subsystem (L1) and the second optical subsystem (L2; L21, L22 ) arranged pupil plane (42) and an image plane (B) in which the image sensor (36) is arranged; b) recording a first image of the object (26, 26'), with only light contributing to the first image that illuminates a first area (A1) of the pupil plane (42); c) recording a second image of the object (26, 26') with the same relative arrangement between the object (26, 26') and the measuring camera (24), with only light contributing to the second image, which has a second area (A2 ) illuminates the pupil plane (42), which differs from the first area (A1), and wherein at least one of the two areas (A1, A2) is not point-symmetrical with respect to an optical axis (52) of the objective (38); d) calculating the surface profile of the object (26, 26') with respect to the optical axis (52) of the objective (38) from a lateral offset between structures (S1, S2, S3) on the first image and corresponding structures (S1, S2, S3) on the second image, characterized in that the second optical subsystem has two optical elements (L21, L22) which are arranged next to each other in a direction perpendicular to the optical axis (52) of the objective (38) and the beam path in two separate partial beam paths, and that steps b) and c) are carried out simultaneously. Procedure according to Claim 1 , whereby the first image and the second image have an overlapping and in particular the same image section. Procedure according to Claim 1 or 2 , in which neither of the two areas (A1, A2) is point-symmetrical with respect to the optical axis (52), but one of the two areas (A1) is point-symmetrical with respect to the optical axis (52) to the other (A2) of the two areas. Procedure according to one of the Claims 1 until 3 , in which the camera has: another image sensor (36 '), a beam splitter (70) between the first optical subsystem (L1) and the second optical subsystem (L2, L21, L22), the beam splitter dividing the beam path into a first beam path leading to the image sensor (36) and a second beam path leading to the further image sensor (36 '). Method according to one of the preceding claims, comprising the following further steps: e) determining a control signal for an adjustment process based on the surface profile calculated in step d), the adjustment process changing the distance between the object (26, 26 ') and the object plane (O) so that a selected plane of the Object (26, 26 ') is located in the object plane (O); f) recording a measurement image with the aid of the image sensor (36; 36'), with light contributing to the creation of the measurement image, which illuminates an area (A3) of the pupil plane that is larger than the first area (A1) and the second area (A2 ). Measuring camera (24) for measuring a surface profile of an object (26, 26'), the measuring camera (24) having: an image sensor (36), a lens (38) which is telecentric at least on the object side, the lens (38) having an object plane (O ), a first optical subsystem (L1), a second optical subsystem (L2; L21, L22), a pupil plane (42) arranged between the first optical subsystem (L1) and the second optical subsystem (L2; L21, L22) and a Image plane (B), in which the image sensor (36) is arranged, has an evaluation device (54) which is set up to determine the surface profile of the object with respect to the optical axis (52) of the lens (38) from a lateral offset (d). to calculate between structures on a first image and corresponding structures on a second image, characterized in that the measuring camera further has two optical elements (L21, L22), which are part of the second optical subsystem and in a direction perpendicular to an optical axis (52 ) of the lens (38) are arranged next to each other and divide the beam path into two separate partial beam paths, and that the first image is recorded with the first partial beam path and the second image is recorded with the second partial beam path. measuring camera Claim 6 , which further has a further image sensor (36 '), a beam splitter (70) which is arranged between the first optical subsystem (L1) and the second optical subsystem (L2, L21, L22), the beam splitter (70) defining the beam path divided into a first beam path leading to the image sensor (36) and a second beam path leading to the further image sensor (36 ').

Images